Digital data is transmitted via serial interfaces in a great number of applications, for example, an Ethernet, a digital telephone system, and various digital audio systems. Power consumption is typically a very important parameter in portable applications, such as, for example, hearing aids. FIG. 1 shows the main components of a digital hearing aid 50. In this example, microphone 52 receives an acoustic wave and transforms the acoustic wave into an analog electrical signal. Analog-to-digital converter (ADC) 54 converts the analog electrical signal into digital form. Digital signal processor (DSP) 56 processes the digital signal according an audiologist's prescription. Then digital driver 58 converts the processed digital signal into an acoustic wave directed toward a patient's ear. Microphone 52, shown in FIG. 2, is generally a capacitive type microphone. Small metal container 62 is sealed on one side (not necessarily an air-tight seal) by conductive membrane 60 which is deflected when an acoustic wave applies force upon the conductive membrane. Conductive membrane 60 and metal container 62 are electrically isolated from one another, and the two-terminal system represents a capacitive structure. An electrical field exists between the two capacitive plates, i.e., between conductive membrane 60 and metal container 62, and a time varying electrical voltage signal is thus created between the two plates when conductive membrane 60 vibrates. This produced electrical signal can provide only a small amount of power, and is therefore sensitive to electrical noise and other disturbances. The metal container is generally connected electrically to the system's ground, for example, a battery's negative terminal. A cavity inside metal container 62 is thereby, to a large extent, shielded from interference from unwanted electrical fields that may surround microphone 52. A small integrated circuit (not shown) located inside metal container 62 amplifies the signal before the signal leaves the shielded environment. In advanced products, the signal is not only amplified, but also analog-to-digital (A/D) converted inside metal container 62. The advantage of this procedure is that digital signals are virtually immune to noise interference, and hence can be routed outside metal container 62 without any loss of performance. Subsequent digital signal processing implemented by DSP circuit 56 should preferably be located outside metal container 62, i.e., the digital signal processing should be separated from noise sensitive circuits near microphone 52.
FIG. 3 shows a system-level electrical schematic of a digital hearing aid where the ADC 54 is placed inside the microphone's metal container 62. The microphone is electrically represented by voltage source 64 with a capacitive output impedance. Inside the shielding metal container are buffer circuit 66, A/D converter 54, and transmitter 68. The system in FIG. 3 further comprises receiver 72, DPS circuit 56, digital driver 58, clock generator 78, and battery 74.
However, such a system suffers various shortcomings which are associated with such data interfaces. Specifically, the small physical size of metal container 62 limits the number of wires that can be used to connect the metal container to other elements in the hearing aid. A typical requirement is that the information-carrying signal be transmitted over single wire interface 76. The physical dimensions of interface 76, however, are far greater than those characteristic of interconnections between circuit blocks on a monolithic integrated circuit Hence, the interface is subject to a substantial capacitive load 70 to ground. Capacitive load 70 is highly undesirable because this substantial capacitive load will cause the transmitter to drain a substantial amount of energy from battery 74 every time interface 76 is charged from a low voltage to a higher voltage. Transmitter 68 will thus consume a significant amount of power if interface 76 is carrying a high bit rate. Therefore, it would be advantageous to have a method and system to substantially reduce the power consumption of the transmitter that will substantially reduce the power consumption without any loss of data.